HM03145 High Efficiency DC/DC Module

APPLICATION INFORMATION
The current limit circuitry also protects against
negative over-current (i.e. when the current is
flowing from the load to PGND through the
inductor and low-side MOSFET). In this case,
when the low-side MOSFET is turned on, the
phase node, (Phase), will be higher than
PGND initially. The HM03145 monitors the
voltage at Phase, and if it is greater than a set
threshold voltage of 125mV (nom.) the
low-side MOSFET is turned off. The device
then waits for approximately 2.5μs and then
LG goes high for 300ns (typ.), once more to
sense the current. This repeats until either the
over current condition goes away or the part
latches off due to output over-voltage (see
Output Over-voltage Protection).
Selection of the Input Capacitor
The input filter capacitor should be based on
how much ripple the supply can tolerate on
the DC input line. The larger capacitor, the
less ripple expected but consider should be
taken for the higher surge current during the
power up. The HM03145 provides the
soft-start function that controls and limits the
current surge. The value of the input capacitor
can be calculated by the following formula:’
In addition to the bulk capacitance, some low ESL
ceramic capacitance is recommended to
decouple between the drain terminal of the high
side MOSFET and the source terminal of the low
side MOSFET, in order to reduce the voltage
ringing created by the switching current across
parasitic circuit elements.
Output Capacitors
The HM03145 is designed for low output voltage
ripple. The bulk output capacitors C OUT is chosen
with low enough effective series resistance (ESR)
to meet the output voltage ripple and transient
requirements. C OUT can be low ESR tantalum
capacitor, low ESR polymer capacitor or ceramic
capacitor. The typical capacitance is 330uF, if all
ceramic output capacitors are used. The
internally optimized loop compensation provides
sufficient stability margin for all ceramic
capacitors applications. Additional output filtering
may be required by the system designer, if further
reduction of output ripple or dynamic transient
spike is required.
C
IN
=
I
×∆t
∆V
IN
Where:
C IN is the input capacitance (uF)
I IN is the input current (A)
Δt is the turn on time of the high-side switch
(us)
ΔV is the allowable peak to peak voltage (V)
TITLE: SPECIFICATION OF HM03145
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